In many fields of endeavor, images are stored for later access and examination. For example, X-ray photographs and other images are stored for later study by medical personnel. Similarly, engineering drawings may be stored for later recall. In each of these applications, as is true in many others, the stored images must be able to be randomly accessed in order to be effectively used. One method of storing such images and allowing random access is to simply store copies of the images on paper or another suitable medium. As the number of such images or documents stored becomes large, however, the space required to so store the images can become great. Furthermore the problems associated with locating a particular image can also be difficult.
An alternative to storing the actual images or documents is the storing of electronic representations of those images from which a computer can electronically reconstruct the image and display it on a suitable device. Typically such systems allow random access to documents by recalling a selected document when a reference number or name associated with that document is typed on a keyboard or keypad. An inherent disadvantage of such a system lies in the fact that the reference numbers or names must be recorded and recalled and correctly entered in order to access selected documents.
A field where easy access to documents is important is that of using images in presentations. Studies have indicated that the use of visual aids, such as transparencies displayed by an overhead projector, can greatly increase the effectiveness of speakers. The effectiveness of a presentation is, however, greatly reduced, or even eliminated, if the speaker must search for a particular transparency. Even when the transparencies are properly ordered at the beginning of a speech, audience interaction or other factors may require the speaker to depart from the prepared outline, inducing such searching.
The use of computer-generated images which may be directly projected by a large screen television or produced on a display such as a liquid crystal display and projected by a conventional overhead projector helps to alleviate problems associated with such searching. A problem that does exist with such systems, however, relates to the way images are accessed. Typically such computerized image display systems permit display of images either in a pre-set sequence, or randomly using a keypad as described previously. If sequential access is used, a speaker must display all images in the predetermined sequence even if some images are to be skipped. Similarly in order to return to a previously displayed image, the speaker must step back through intervening images until the desired image is reached. Alternatively, if an image code is entered through a keypad the speaker must remember the code associated with a particular image and correctly enter it on the keypad in order to cause the image to be displayed. Entry of an incorrect image could cause the wrong image, or no image, to be displayed. Even if only correct images are displayed the pause which occurs while the access code is entered may be distracting to the audience.